1. Cross-Reference to Related Applications
Not applicable.
2. Field of the Invention
The present invention relates generally to disk drives, and in particular to a disk drive including surface coated disk clamp screws with reduced coefficient of friction for mitigation disk clamp movement.
3. Description of the Prior Art
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes the disk drive base, a cover, at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA).
The head stack assembly has an actuator assembly having at least one head or slider, typically several, for reading and writing data to and from the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached sliders are moved relative to tracks disposed upon the disk.
The spindle motor includes a spindle motor hub that is rotatably attached to the disk drive base. The spindle motor hub has an outer hub flange that supports a lowermost one of the disks. Additional disks may be stacked and separated with annular disk spacers that are disposed about the spindle motor hub. A disk clamp is affixed about the spindle motor hub. Fasteners, such as screws, are disposed through screw openings of the disk clamp and engage threaded disk clamp holes that are circumferentially spaced about a periphery of the spindle motor hub for applying a clamping force by the disk clamp against the topmost disk to secure all of the disks to the spindle motor hub.
The spindle motor typically includes a spindle motor base that is attached to the disk drive base. A shaft is coupled to the spindle motor base and the spindle motor hub surrounds the shaft. The spindle motor hub may be rotatably coupled to the shaft, and therefore the spindle motor base, typically via a pair of bearing sets. A stator is positioned about the shaft and is attached to the spindle motor base. A magnet element is attached to the hub flange. The stator includes windings that selectively conduct current to create a magnetic field that interacts with the various poles of the magnet element. Such interaction results in forces applied to the spindle motor hub that tend to rotate the spindle motor hub and the attached disks.
The various rotating elements associated with the disks may be referred to as a disk pack. This may include not only the disks, but also the rotating portions of the spindle motor, the spacers, the disk clamp and disk clamp screws. It is crucial that the mass of the disk pack is balanced so as to minimize dynamic vibrations during operation of the disk drive. The greater the magnitude of the imbalance, the greater the degradation of the disk drive performance, not only in terms of read/write errors, but also seek times. A significant amount of imbalance may even result in damage or excessive wear to various disk drive components.
A problem with balancing of the disk pack arises upon the final installation of the disk clamp screws. The torquing of the disk clamp screws may lead to a shifting of the disk clamp relative to rest of the disk pack. Such shifting of the disk clamp may result in a shifting of the location of the disks, resulting in a significant imbalance of the overall disk pack. In this regard, there is a need in the art for an improved disk drive including a disk clamping arrangement in comparison to the prior art.